Shift Light: Testing and Inspection

Chart C-8B:

Wiring Diagram For M/T Shift Light:

CIRCUIT DESCRIPTION:

The shift light indicates the best transmission shift point for maximum fuel economy. The light is controlled by the ECM and is energized by grounding circuit 456. The ECM uses the measured engine and the vehicle speeds to calculate what gear the vehicle is in. It's this calculation that determines when the shift light should be energized. The ECM uses information from the following inputs to control the shift light:

1. Coolant temperature Sensor (CTS)
2. Throttle Position Sensor (TPS)
3. Vehicle Speed Sensor (VSS)
4. Engine Speed



TEST DESCRIPTION: The numbers below refer to circled numbers on the diagnostic chart.

1. This should not turn "ON" the shift light. If the light is "ON", there is a short to ground in wiring circuit 456, or a fault in the ECM.
2. When the diagnostic terminal is grounded, the ECM should ground circuit 456. This should turn "ON" the shift light.
3. This checks the shift light circuit up to the ECM connector. If the shift light illuminates, then the ECM does not have the ability to ground the circuit.